1. Technical Field
The present disclosure relates to a lighting system, and more particularly, to a lighting system for emitting light using power having a phase controlled by a dimmer and improving the light emission state of a light source and a control circuit for the same.
2. Related Art
A lighting system has been developed to use a light source having high emission efficiency using a small amount of energy in order to reduce energy. A representative light source used in the lighting system may be a light-emitting diode (LED).
The LED is advantageous in that it is different from other light sources in various factors, such as energy consumption, life span, and light quality. The LED is characterized in that it is driven by a current. Accordingly, a lighting system using LEDs as a light source is problematic in that it requires many additional circuits for current driving.
In order to solve the problem, a lighting system has been developed to supply AC power to LEDs in an AC direct type. The lighting system of the AC direct type is configured so that the LEDs emit light by converting the AC power into a rectified voltage and performing current driving using the rectified voltage. The lighting system of the AC direct type is characterized in that it has an excellent power factor because it uses the rectified voltage without using an inductor and a capacitor. The rectified voltage refers to a voltage obtained by performing full wave rectification on the AC voltage through the full wave rectification of a rectifier.
Furthermore, the lighting system may include a power circuit for supplying a rectified voltage using an AC power source and a power control unit for performing current control for driving a light source in response to the rectified voltage. In general, the power control unit may be fabricated in a single chip type and mounted on the lighting system.
In the lighting system, the power circuit may be configured to have a dimming function. The dimming function may be implemented by a dimmer adopted in the power circuit. The dimmer is configured to determine the location where the phase of an AC voltage is triggered in response to a change of an internal charging voltage. That is, the dimmer may output an AC voltage having a phase controlled, and a light source emits light with luminosity corresponding to the phase-controlled AC voltage.
The dimmer may control the luminosity of the lighting system from a turn-off level of the light source to a maximum light-emission level depending on performance of the lighting system. If the dimmer has a hysteresis characteristic, it may have power supply efficiency of 20˜80%. If the dimmer does not have a hysteresis characteristic, it may have power supply efficiency of 5˜95%.
In general, the dimmer is problematic in that compatibility is low depending on a load due to a difference in the characteristics of an internal diac or triac. From a viewpoint of the dimmer, a power control unit for performing current control for driving a light source may serve as a load.
If a load having a resistance characteristic is applied, the dimmer may have excellent characteristics. An example of a load having a resistance characteristic may include an incandescent, which may be defined as a linear load.
The dimmer has limited compatibility in accordance with a load, such as a power control unit having reactance or a power control unit for performing current regulation corresponding to the AC direct type. An example of the load having reactance may include a Flyback or Buck type power control unit. As described above, the power control unit having reactance or the power control unit for performing current regulation corresponding to the AC direct type may be defined as a nonlinear load.
The dimmer is limited in providing AC waveforms of high quality in accordance with the nonlinear load. More specifically, the dimmer may provide an output voltage that has been irregularly delayed due to an RC characteristic. Furthermore, the dimmer may provide an output voltage having a varying width in which turn-on is maintained by the operating characteristics of a triac (i.e., a turn-on width). In particular, a positive output voltage and a negative output voltage may have different turn-on widths. Furthermore, the dimmer may provide an output voltage so that positive output and negative output have different sizes (or amplitudes).
Accordingly, in a lighting system that adopts the dimmer and uses the nonlinear load, a light source may not maintain uniform luminosity due to the unstable operating characteristic of the dimmer. In particular, if AC power is supplied to a light source in the AC direct type, the light source may emit light so that the light is irregularly shaken due to the output voltage of the dimmer having different positive output and negative output sizes. A phenomenon in which luminous intensity is irregularly changed and shaken in the light-emission state is called shimmer. In particular, the shimmer may become worse when a light source emits light with low luminous intensity.
Accordingly, in order to implement a dimming function using the dimmer, a lighting system having a nonlinear load needs to stabilize the light emission state of a light source.